This invention relates a sheet formed into a rugged shape (hereinafter referred to as "rugged shaped sheet") and a process for manufacturing the same, and more particularly to a rugged shaped sheet improved in non-slip and aesthetic properties and a process for manufacturing the same.
Conventionally, it has been attempted that sneakers or sports shoes used as jogging shoes, basketball shoes, tennis shoes or the like are constructed into a multi-layer structure by forming an outer sole which is a lowermost layer of a shoe sole contacted with the ground or a floor of a solid rubber material or a high-density sponge material and laminating at least one sponge sheet of a light-weight material exhibiting satisfactory cushioning properties such as ethylene vinyl acetate (EVA) on the outer sole, to thereby accomplish a decrease in weight and an improvement in shock absorbing properties.
The solid rubber or high-density sponge is relatively rigid and exhibits satisfactory ground gripping properties and wear-resistant properties; however, it is increased in weight, to thereby fail to reduce the weight of the shoes.
In view of such a problem, various kinds of techniques of forming a satisfactory shoe sole while improving a material for the shoe sole are proposed. For example, there is proposed a method wherein a polyurethane resin film like a nonwoven sheet and a liquid polyurethane compound for forming non-slip projections are put in a mold and then subjected to thermal cure, resulting in being integrally bonded. The method proposed is disclosed in Japanese Patent Application Laid-Open Publication No. 310601/1989. Another method which is likewise proposed comprises the steps of arranging a perforated plate on a nonwoven fabric material to keep both intimately contacted with each other, pouring a polyurethane elastomer material containing a thickening agent into the perforated plate, carrying out a squeezing treatment with respect to the elastomer and heating the elastomer to cure it, resulting in forming an embossed sheet. The method is entitled a "method for manufacturing an embossed sheet" and is disclosed in Japanese Patent Application Laid-Open Publication No. 185822/1992 by the assignee.
Unfortunately, an improvement in the material for the shoe sole taught in the proposed methods is insufficient to provide the shoe sole with satisfactory non-slip properties. In order to permit the shoe sole to exhibit increased non-slip properties, it is further required to consider other factors in addition to the material for the shoe sole, such as, for example, a height of a rugged pattern formed on the sole of the sports shoes, an area of the rugged pattern contacted with the ground, a configuration of a surface of the rugged pattern contacted with the ground, arrangement of the pattern and the like. However, consideration of the factors causes a configuration of the rugged pattern to be complicated. Therefore, manufacturing of the shoe sole with the rugged pattern of such a complicated configuration by means of a mold as proposed in Japanese Patent Application Laid-Open Publication No. 310601/1988 causes a manufacturing cost of the mold to be extensively increased.
Also, the above-described method proposed in Japanese Patent Application Laid-Open Publication No. 185922/1992 by the assignee wherein a rugged pattern is formed by the single perforated plate is conveniently applied when a configuration of the rugged pattern is relatively simple, however, it is not suitable for the rugged pattern of such a complicated configuration as described above.
Further, a rugged pattern formed on a sole of sports shoes is generally made of the same material as the sole in a manner to be integral with the sole. It is often desired to locally vary properties of the rugged pattern in order to enhance the non-slip properties and aesthetic properties of the sole. However, the above-described formation of the rugged pattern integral with the sole fails to significantly vary the properties of the rugged pattern.